Hurricane Harvey in 2017 and Hurricane Beryl this past week, both followed similar tracks prior to their landfall in the US near Houston. They both formed in the Atlantic before traveling westward through the Caribbean, traversed the Yucatan Peninsula where they weakened considerably, and then reintensified and made landfall on the Texas coastline. Despite these similar tracks, the two storms have resulted in very different outcomes. Harvey resulted in economic losses of almost $160Bn (2023 dollars, source: NCEI) and insured losses of almost $38Bn (2023 dollars, source: III), while Beryl thankfully looks to have caused just a small fraction of that. What created such different outcomes despite similar paths prior to landfall?
Given the very similar tracks it may seem logical to conclude that both Harvey and Beryl should have behaved similarly over the Gulf of Mexico. However, while Harvey strengthened from a tropical depression to a category 4 hurricane, Beryl only managed to strengthen from a tropical storm to a category 1 hurricane. Two major reasons drove this different behaviour.
The first reason was sea surface temperatures, which are a well-known driver of hurricane strength – warmer oceans allow for stronger hurricanes. Sea surface temperatures in the Gulf of Mexico near where Beryl travelled were quite warm in an historical context. The early-July sea surface temperatures this year would have been unprecedented before 2000 and were the 5th warmest on record for this time of year since 1982. However, relentless climate change means the 2024 temperatures were only slightly above the mean temperatures of the last 10 years. Hurricane Harvey occurred at the end of August 2017. Sea surface temperatures in its track in the Gulf of Mexico were warmer than those encountered by Beryl (29.9°C for Harvey vs. 29.5°C for Beryl), largely due to Harvey occurring later in the year, when sea surface temperatures are typically warmer. However, these sea surface temperature differences likely do not explain the entirety of the difference in storm behaviour over the Gulf of Mexico. The second major reason for their differences was the amount of dry air in the Gulf of Mexico while they made their way towards Texas. Dry air helps limit hurricane intensification; Hurricane Beryl encountered relative humidity values of ~40%, while Harvey had values near ~60%. These differences helped limit the strengthening of Beryl and spared the Texas coastline from a stronger hurricane landfall.
It’s also worth noting that Harvey caused exceptional flooding when it stalled after landfall. Beryl thankfully exited the Houston area much more quickly helping to limit the flooding.
As we continue to monitor US Hurricane season, sea surface temperatures will be a big focus, but Beryl was a good reminder that other factors, such as the atmospheric moisture content and steering flows, matter too.
